The present invention relates to the electrical, electronic and computer arts, and, more particularly, to correcting perspective distortion.
In photography, perspective distortion is a warping or transformation of an object and its surrounding area that differs significantly from what the object would look like with a normal focal length, due to the relative scale of nearby and distant features. Perspective distortion is determined by the relative distances at which the image is captured and viewed, and is due to the angle of view of the image (as captured) being either wider or narrower than the angle of view at which the image is viewed, hence the apparent relative distances differing from what is expected. When taking a self-portrait photo (“selfie”) using a mobile camera (e.g., integrated with a smart phone), due to the small focal length of the mobile device, and the limited distance (e.g., arm reach) the images are distorted (e.g., “fish eye effect” or “barrel distortion”). This is a form of extension or wide-angle distortion, in which an object close to the lens (e.g., the subject's face) appears abnormally large relative to more distant objects, while distant objects appear abnormally small and hence more distant.
One solution is to mount the mobile device further away and use a timer activated camera mode. However, there are several limitations to this approach. The mobile device may fall and get damaged if the mounting is not secured well. Especially in crowded places, there is a risk of device theft or incidental damage to the unattended device. Directional mounting of the device can be difficult, as part of the objects of interest (e.g., the subject of the photograph) is not in the frame during the mounting process. Also, timing control of the camera is limited compared to direct instantaneous control of the shutter.
Another option is to ask another person to take a photograph on one's behalf. However, there are again limitations to this approach. A stranger may steal the device. Sometimes, no person can be found available to take the photograph. Also, the photographer may not be familiar with the operation of the camera on the mobile device and as a result either fail to take a photo, or take a photo which out of focus, out of frame, or without an adequate level of brightness.
Alternatively, one can use a selfie-pole, although this solution is cumbersome. Also, one may wish to take a self photo from a perspective where the mobile device cannot be mounted (e.g., up in the air). Another approach is to have a remote controlled drone equipped with a camera. This option can be problematic in small places, and may involve safety issues. This approach also requires special equipment (e.g., a drone), and flying drones while capturing images typically requires experience and skill.
A further option is image correction with an ISP (image signal processor). However, this requires the lens geometry to be programmed into the device so that a correction can be made. Also, the system (which is not mobile) is generally designed for IP (internet protocol) cameras. This solution applies a fixed correction to the image, and cannot incorporate a desired perspective and/or various distances of the object. An additional option is software correction to reverse the distortion effect. This requires inputting geometrical knowledge of the camera lens, and potentially chromatic information regarding the lens. However, a single image is considered, without considering the orientation of the camera or the subject. Thus, it is not possible to define a desired perspective. Also, a fixed correction is irrespective of the actual distortion.